Instead, the Wyoming Republican’s amendment replaces the House directive for a deficit-neutral tax cut with one that could add up to $1.5 trillion to the deficit over 10 years, similar to the Senate’s.

The amendment strips language requiring the reconciliation measure to go through the House Budget Committee, allowing the Ways and Means Committee to send a tax overhaul bill straight to the floor

The objective of the changes worked out with House leadership is for the Senate to be able to adopt a budget that is acceptable to the House, negating the need for a conference committee to iron out differences.

The amendment duplicates within the House budget resolution a reserve fund in the Senate budget that allows for an appropriations deal to raise the discretionary spending caps, including the Senate notation that the defense cap could be raised to $640 billion for fiscal 2018. As is the case with the Senate rule, the provision allows the caps to be raised without their additional cost being offset, unlike past budget deals.

Enzi’s amendment also literally strikes out language favored by the House GOP regarding a reserve fund for the privatization of air traffic control.

The air traffic control issue has been a major sticking point between the two chambers on efforts to reauthorize the Federal Aviation Administration.

The amendment also includes other existing provisions in the House budget resolution that House lawmakers want in the budget resolution adopted by both chambers.

The Senate moved Thursday night toward adoption of the fiscal 2018 budget resolution, which will serve as a vehicle for a tax code overhaul — an effort that still has major obstacles ahead of it.

Republican leaders want to finalize a joint budget resolution as quickly as possible so they can move onto introducing the tax bill, which would then move under reconciliation procedures and reduce the typical 60-vote Senate hurdle to a simple majority.

After beginning consideration of the fiscal blueprint Tuesday and using up the available 50 hours of debate time, the Senate at 3 p.m. began the vote-a-rama where unlimited amendments are allowed.

Greasing the wheels

Under the Senate resolution, the Finance Committee would be asked to write a tax cut that increases the deficit by up to $1.5 trillion over a decade.

The House budget contains reconciliation instructions directing the Ways and Means Committee to write a tax bill that is deficit-neutral, meaning that tax cuts would have to be offset with other tax increases or with spending cuts. In fact the House version, which the Senate was voting to amend Thursday and which will serve as the vehicle for the final resolution, instructs Ways and Means to reduce the deficit on net by $52 billion over a decade. That provision would be dropped in the amendment Enzi is set to offer, with House leadership's blessing.

While the House can take advantage of dynamic scoring to help make its tax bill balance, that form of cost estimation that calculates the effect of a bill on economic growth may not be possible in the Senate because of that chamber’s unique rules.

GOP senators acknowledged they see the sole purpose of the budget as providing a path to a tax cut through the reconciliation process, which would permit a tax bill to pass with a simple majority in the Senate.

Several senators noted that the discretionary toplines in the plan — which would limit fiscal 2018 defense spending to $549 billion and nondefense to $516 billion — have little meaning since most Democrats as well as Republicans see those limits as too low.

Senate Armed Services Committee John McCain railed against the defense limit, saying constraints on military spending are partly responsible for a rash of training accidents have killed dozens of troops.

“We have seen the steady degradation of the military,” the Arizona Republican said. “The strain of constant operational tempo, combined with inadequate and unstable funding has over the past 16 years worn down the greatest military in the world.”

McCain said the only solution is for Congress to negotiate a bipartisan deal to raise the cap on defense spending. GOP and Democratic leaders and the White House have begun to negotiate a deal to raise the defense and nondefense caps, likely for two years, people with knowledge of the talks told CQ.

Meanwhile, Kentucky Republican Sen. Rand Paul, alone among the caucus, threatened to vote against the budget over his opposition to war funds that would are estimated to cost $43 billion in fiscal 2018 outlays.

Paul’s amendment to cut an equal $43 billion in discretionary spending in fiscal 2018 was rejected on a 5-95 vote. Another Paul amendment, which was defeated 4-94, would have added reconciliation instructions to nine authorizing committees directing them to reduce the deficit or cut spending by $97.9 billion in fiscal 2018 alone.

President Donald Trump predicted success for the budget Thursday afternoon, after expressing uncertainty about the vote earlier in the day. “I think we'll be successful tonight and it will be possibly sometime in the morning, maybe sooner,” he said. “I think we have the votes for the budget, which will be phase-one of our massive tax cuts and reform.”